Heretofore, small-sized X-ray generation devices have been used in industrial nondestructive testing, testing for animals such as pets, and dental diagnoses. Among those, X-ray generation devices of a type called mono tank or mono block have been used in which an X-ray tube and a high-voltage generation unit are mounted inside a single housing (see Patent Document 1, for example).
FIG. 9 shows one example of the mono-tank X-ray generation device. This X-ray generation device (mono tank) 1X includes, inside a housing 8, an X-ray tube 2 and a high-voltage generation unit 3 configured to supply power to the X-ray tube 2. Further, insulating oil 4 is filled inside the housing 8. The X-ray tube 2 includes an anode 5 and a cathode 6. Moreover, an anode heat radiator 17 is arranged on the anode 5 of the X-ray tube 2. Further, the X-ray tube 2 is surrounded by insulators 21 and 31 and an X-ray shielding member 32 for preventing scattering of X rays. Note that L1 indicating a broken line represents the path which thermal electrons and an X ray for irradiation travel; 7, an X-ray irradiation window; 23, an X-ray irradiation flange, and F, a focal spot.
Next, an operation of the X-ray generation device 1X will be described. First, the high-voltage generation unit 3 applies voltages of from 10 kV to 500 kV to the X-ray tube 2. Specifically, +50 kV and −50 kV, for example, are applied to the anode 5 and the cathode 6, respectively (a voltage difference of 100 kV). With this electricity, a filament, which is the cathode 6 of the X-ray tube 2, lights up and emits thermal electrons. The thermal electrons collide with the anode 5 on the opposite side (this spot is the focal spot F). The energy of this collision generates an X ray. This X ray is taken out to the outside through the X-ray irradiation window 7 as an X ray for irradiation L1, and then put into use.
During this operation of the X-ray generation device 1X, the X-ray tube 2 and the housing 8 are at ±50 kV and ±0 V, respectively, for example. This potential difference may possibly cause electric discharge (spark). To prevent this electric discharge, the insulators 21 and 31 are disposed around the X-ray tube 2, and the insulating oil 4 is filled. For these insulators 21 and 31, a resin resistant to the insulating oil or a ceramic is used. Note that the insulating oil 4 also has a function of cooling down the X-ray tube 2, in addition to the function of preventing the electric discharge.
Meanwhile, since the X ray scatters radially at the focal spot F on the anode 5, X rays may possibly be emitted in all directions in the X-ray generation device 1X. To prevent exposure to such X rays, the X-ray shielding member 32 is disposed around the X-ray tube 2. For this X-ray shielding member 32, lead is used in general for its high X-ray shielding effect.
The X-ray generation device 1X described above has some problems. Firstly, it has a problem that lead is used for the X-ray shielding member 32. Lead is harmful to the human body and, when wasted, adversely affects the natural environment. Thus, it is desirable not to use lead. To replace lead, it is possible to use tungsten which has a high X-ray shielding rate. However, tungsten is expensive, costing about 12,000 yen to 15,000 yen per kilogram.
Secondly, the X-ray generation device 1X has a problem that there is a limitation in its miniaturization. This is because the X-ray generation device 1X needs the X-ray shielding member 32 of a sufficiently large thickness for shielding the scattering X rays, and also because the X-ray generation device 1X needs the insulators 21 and 31 of a sufficiently large thickness for preventing the electric discharge. Note that the X-ray shielding effect is proportional to the thickness of the X-ray shielding member 32. Likewise, the insulating effect is proportional to the thickness of the insulators 21 and 31.